Electrolytic plating is widely used for plating of microelectronic and other precision articles. For example, electroplating is widely practiced in the printed circuit industry to add layers of various metals to other conductors. Copper may be plated to increase the thickness of conductors. Layers of nickel and gold are routinely added to copper for protection to prevent oxidation. A great variety of materials, thicknesses and layers are known in the electroplating art.
An important and major concern in electroplating is control of plated thickness distribution. It especially impacts the conventional pattern electroplating of circuits, on printed circuit boards or on semiconductors, where isolated circuits plate thicker than dense circuits.
Plating thickness is also related to the current distribution during the plating operation. Printed circuit or plated feature density also affects the uniformity of the plating in a given region.
One suggestion for improving thickness distribution has been pulse reverse plating. However, this involves significant investments in new rectifiers and cabling, and the use of different plating chemistries than when DC is used.
Attempts to minimize disparity in plating thicknesses have also involved changing the cross-sectional area of plating rack bus bars. However, tailoring the bus bars' geometry is difficult to implement in an actual rack due to the extra bus bar mass that is needed in the lower current regions to reduce the voltage drop between contacts and the design complexity this generates.
It would therefore be desirable to provide for improving the thickness distribution in electroplating.